I've been using Symlinks on Windows for months and the work GREAT for me, but now Unity has just announced that Unity 4 will intentionally disable support for symlinks on Windows. They were already disabled on OSX. I've tried to communicate with Unity people that this is a big pain, but the only response I've received is that they "create problems", but I've never heard anything more concrete than that.
Symlinks are incredibly useful because the allow you to share source files between multiple projects. In my case, I'm creating an open-source code library for Unity which I'd like to be able to test AND edit in multiple projects without having to manually copy files or deal with glitchy git submodules.
I'm not even asking for Unity to turn them on for everyone, I'd just like some sort of option or configuration flag somewhere that'll allow users to turn them on intentionally if they need them.